John I Tzimisces was the lover of Empress Theophano, which led to the murder of Emperor Nicephorus II and John's elevation to the throne. John introduced a follis that depicted a bust of Christ on the obverse and a religious inscription on the reverse. These types, referred to as anonymous folles because they do not identify the issuing emperor, would become the norm for bronze coinage during the following century.

I believe your follis is one of his successors Basil II and Constantine VIII. John had no ornaments after the phrase. Yours does, and thus falls into the large majority of anonymous folles. @Valentinian made a good article on them recently. Here is my follis, which was also my first Byzantine coin.